Film guiding mechanism



Mayl, 1935.

J. D. BASSON FILM GUIDING MECHANISM 5 Sheets-Sheet 2 Filed Jan. 14, 1931lNvENToR Joseph llason, BY

m inslaan- 00M, @w57 5M ATTORNEYS May 2l, 1935. J. D. BAssoN 2,002,074

FILM GUIDING MECHANISM Filed Jan. 14, 1931 3 Sheets-Sheet 3 lf: 1 l g31a l i l l i i0 31 l I l S/ g g z i l 'l l J@ lNvENToR Lasqv/z/ assanBY A1ToR EYs Patented May 21, 1935 UNITED STATES PATENT OFFICE ',sclaims.

My invention relates to an arrangement or mechanism whereby a iilm intape or web form is caused to traverse a selected path while moving pastor with respect'to an aperture traversed by 8 a light beam; moreparticularly, such an arrangement or mechanism is adjustable so that thefilm path may be obliquely related as desired with respect to theoptical axis of an objective lens traversed by said light beam.

More particularly, my invention relates to a projector mechanism andinvolves an arrangement whereby motion picture film traversing theprojection field of such mechanism is caused to move at a desiredoblique angle with respect to the optical axis of the objective lensthereof.

My inventionv also relates to an arrangement whereby a lm, as aforesaid,is passed between adjustable members so as to be under suitable tensionwhile moving past or with respect to the aforesaid aperture.

My invention relates to an arrangement of the character stated which issimple, practical and highly satisfactory in operation.

Further advantages, objects and characteristics of my invention willbecome apparent from the following description taken in connection withthe accompanying drawings.

For an understanding of my invention and for an illustration of one ofthe many forms thereof, reference is to be had to the accompanyingdrawings, in which:

Figure 1 is a diagrammatic view generally illustrative of my invention;

Fig. 2 is a rear elevational view of a film trap assembly; Fig. 3 is alongitudinal, vertical sectional view, partly in elevation, oi themechanism shown in Fig. 2;

Fig. 4 is a -front elevational view of a part of the mechanism shown inFig. 3;

Fig. 5 is an enlarged, longitudinal, vertical sec tional view, partly inelevation, of a part of the mechanism shown in Fig. 2;

Fig. 6 is a transverse, vertical sectional View, partly in plan, and istakencn the line 6--6 oi Fig. 3 looking in the direction of the arrows;

Fig. 'l is a perspective view4 showing a plurality of passage-formingmembers in disassembled relation; 1

Fig. 8 is a diagrammatic view generally illustrative of my invention;and

Fig. 9 is a diagrammatic view illustrative of a phase oi' Arnyinvention. v

In the projection art and, more particularly, the motion pictureprojection art, correct image focus,

(ci. ca -11) in the absence oi corrective measures, is not obtainable ona vertical screen when the optical axis of the objective or projectionlens is obliquely related to the screen.

Thus, in Fig. l, the line L is shown as disposed at right angles to asuitable projection screen, not shown, -but asumed to be verticallydisposed in an auditorium or the like, said line L intersecting thecenter of the screen. Any suitable projection lens-P is shown aspositioned l0 to one side of the line L and this projection lens is sorelated to the screen that the optical axis Li intersects said screen atapproximately the point of intersection therewith o'f the line L. Fromthe foregoing, it follows that the optical 15 axis LI of the projectionlens P is obliquely related to the aforesaidr screen.

As stated, the projection lens P is disposed to one side of the screencenter line and the relation may be such, i! desired and as shown, thata plane which includes the lines L and Ll is approximately horizontallydisposed although it shall be understood that the projection lens P maybe either above or below the line L to a desired extent whereby a planeincluding said lines L and Ll is inclined either upwardly or downwardlyas the case may be.

As diagrammatically illustrated in Fig. 1, the system is shown asutilized i'or the projection of motion pictures, the motion picture nlmbeing indicated at A. As thus shown, the film A, assuming horizontaldisposition of the sheet on which the drawing is made, travelsvertically through the projection field and the axis Ll is at rightangles with respect to said nlm.

Under such circumstances, it results, when the axis LI is obliquelyrelated to the screen as stated, that correct screen image focus is notobtained and, therefore', in accordance with my invention, the iilm A,in any suitable manner, is 40 caused to move through the projectionfield along a path such, for example, as indicated at AI which, however,is still vertical, assuming horizontal disposition oi the sheet on whichthe drawing is made. It results, therefore, that the 43 new path of thenlm, namely, that indicated at Al is obliquely related to the opticalaxis LI or, in other words, that any given illm section, while in theprojection ileld, is in a partly rotated position with respect in thescreen whereby correct image focus is obtained.

The mechanism for obtaining the result noted above may asume a varietyoi forms. One form which has proven satisfactory in practice is hereinshown in Figs. 2-1 as comprising the film trap 55 assembly of a devicewell known in the prior art, this assembly comprising members I and 2detachably secured together in a suitable manner, not shown, to form apath or track for the motion picture film F, or equivalent. The member Icomprises a flange Ia by which the film trap assembly is secured inproper position to the center frame of the projector.

Carried by the member I is a. transverse, freely rotatable shaft 3 onwhich are mounted sleeves 4 and 4a carrying, respectively, the wheels 5and 6, each of which extends through a slot formed in the member I, thefilm F passing between and being guided by the wheels 5 and 6. Thesleeve 4 is pinned to the shaft 3 and, therefore, is rotatabletherewith. The sleeve da, however, is freely rotatable on the shaft 3and is also movable axially thereof against the force of a spring lcoiled around said shaft 3, one end of said spring 'I engaging one endof the sleeve 4a and the other end thereof engaging the adjacent shaftbearing. The spring i tends to bias the sleeve da and wheel d from leftto right, Fig. 2, whereby the sleeves d and da. are disposed inend-to-end abutting relation. However, under the infiuence of the film Fpassing between the wheels 5 and 6, the latter wheel may be moved fromI'ightvto left, Fig. 2, for a slight distance as determined by theadjacent slot wall, the spring 1 being compressed during this action.A

rIheI member I is provided Awith slots through winch extend,respectively, the usual tension pads 8 and for the film F, each padbeing biased from left to right, Fig. 3, by a spring i!) carried by themember I and engaging therewith.

In accordance with mv invention, the member i comprises a transversepassage or opening Ib in which a passage-defining member il is movablysupported. As herein illustrated and preferably, the memberV ii is`movably supported as just described because spring seated, this seatingarrangement being of Vany suitable character such, for example, as isconstituted by spaced leaf springs i2 and I3 carried bythe member I andengaging, at their respective free ends, opposite sides ofsaid member IIwhereby the latter is biased in a direction from left to right, Figs. 3and 5.. l

Preferably and in accordance with my invention, the passage-formingmember II presents a concave surface to the lm F, the advantages of thisarrangement being hereinafter pointed out. iThe vaforesaid member 2comprises a transverse passage or opening 2b substantially alined withthe passage Ib in the member I and, in accordance with one form of myinvention, this passage 2b is adapted to receive a passage-definingstructure f which constitutes the aperture of the projection system. Asherein shown although not necessarily, the aforesaid passagedefiningvstructure comprises a pair of passagedening members I and I5, thelatter, in the example shown, defining the aperture of the projectionsystem and the former presenting a convex surface which mates with theaforesaid concave surface of the passage-forming member iI. To the endthat the two passage-defining members I4 and l5 may be secured together,the

aperture of the member I4 is arranged to be somewhat larger than that ofthe member I5 whereby the latter may seat upon theformer as shownparticularly in Figs. 3 and 5. For retaining the member `I5 in thisseated relation, there may be utilized'leaf springs IG'and ITI, eachfreely pivoted to the member 2 in such manner that they may bepositioned as shown in Fig. 4 whereby they engage opposite sides of themember I5 and hold it rmly in seated position.

As clearly shown in Fig. 5, the aforesaid passage-defining member I4 isreceived in the aperture 2b of the member 2 and, in accordance with myinvention, said member I4 is adjustable with respect to said member 2.Any suitable arrangement may thus be utilized such, for example, asherein shown wherein a pair ofkscrews I8, I8a extend freely throughpassages provided in the member 2 above and below the transverse passage2b, said screws being threaded, respectively, into the upper and lowersections of the member it, Fig. 5.- At opposite sides of the transversepassage 2b, the respective screws I9, I9a are threaded through and tothe member 2, said last named screws coacting, respectively, withopposite side sections of the member I4.

The film trap assembly is shownin Fig. 3 in its normal operativeposition, the lm F traveling in the direction of the arrows and a givensection thereof engaging, in succession, a continuously driven sprocket20, the path defined by the film trap assembly, an intermittently drivensprocket 22, and a continuously driven sprocket 23. Accordingly,individual frames or sections of said film F are successively broughtinto lregistering relation with the aperture defined by thepassage-forming kmember I5 which, as stated,

forms theaperture of the projection system and throughwhich theprojecting light beam passes from left to rightd as the parts arepositioned in Figs. 3, 5 and 6. Y

- Referring particularly to Fig.` 6, .the line L3 represents the opticalaxis of the projection lens (the same as in connection with the line LIof Fig. 1) while the line L4 isA shown as extending perpendicular tothat film section in alinement with the projection aperture. If the filmsection is so moved that the line Ld is brought into coinciding relationwith the line L3, then said film sectionwould be at right angles to theoptical axis of the projecting lens but, since said lines are angularlyrelated, it follows that saidv film section is obliquely related to theaforesaid optical axis of the projecting lens, This is a characteristicfeature of my invention as heretofore explained in connection with Fig.1.`

The above described obliquev relation of the film section obtains due tothe fact that the passage-forming members I ll and I5 have beenangularly adjusted as a unit in a clockwise direction, Fig. 6, about anaxis defined substantially by a straight line joining the screws I8 and18a. This angular adjustmentl exists due to the fact that the screw i9is threaded throughthe member 2 to less extent than is the screw I9a.AsY stated, the passage-forming member II is spring seatedand,therefore, this member freely assumes an angular position incorrespondence with and as imposed thereon by the member I4.Accordingly, it follows that the path to be followed by the film as itmoves with respect to' the aperture of the projection system isobliquely related to the optical axis of the projection lens and,obviously, this 'may be varied as desired by suitably adjusting thescrews I9 and I9a.

Since the path of the film past the projection aperture is thusobliquely related to the optical axis of the projection lens, it followsthat one edge of the film is nearer the center line of the projectionlens vthan is the other film edge. One edge of the film, therefore, isnear and 'the other edge is "far", the near edge being nearer the lenscenter line and, as the parts are positioned in Fig. 6, it is the upperiilm edge which is the near edge and the lower film edge which is thefar edge. It has been demonstrated in practicing my invention that thefilm, while passing through the film trap assembly, tends to shiftlaterally in a direction leading toward the near edge. For this reason,the arrangement should be such that the near edge of the nlm and thewheel I (which is pinned to the shaft 3 through the sleeve l) are at thesame side of the film trap assembly, whereby the film tends to shiftlaterally toward that guide wheel which is non-movable axially of theshaft 3. Should the arrangement be such that the movable wheel 8 and thenear edge of the film are at the same side of the film trap assembly,the lateral iilm shift causes the wheel B to operate in a permanentlyshifted position, this being contrary to the intended operation of saidwheel.

As hereinbefore stated, the passage-forming member ii may present aconcave surface to the film, the passage-forming member I4 which matestherewith presenting a convex surface to said film whereby the latter,as it traverses the projection aperture, takes a configuration such asshown in Figs. 3 and 5 whereby the film section in the projectionaperture at any given time has a shape corresponding with a peripheralsection of a cylinder. This is advantageous because that film section inthe projection held at any given time is so curved that the centerthereof is further from the screen than are the top and bottom edgesthereof. Accordingly, better focus exists on the screen than is the casewhen the film section in the projection field is oi plane configuration.The cylindrical film shape is also advantageous because somewhatincreasing the tension of each film section while passing through theprojection field to thereby overcome or decrease film irregularities. Itshall be understood, however, that the members il and i4, or equivalent,may be of such different shape as desired whereby the film may be ofsubstantially plane configuration while passing through the projectionaperture.

As is well understood to those skilled in the art, the members I andlare detachably but positively retained in the relation shown. Bymanipulating suitable mechanism, not shown, the member 2 may be movedfrom the member l when it becomes necessary to rethread the film or togain access to the interior of the film trap assembly.

Referring to Fig. 8, P2 and PI represent a pair of projectors of `anysuitable type such, for example, as are ordinarily utilized forcommercial front projection. In the example shown, although notnecessarily, the projectors P2 and P3 are focused upon the rear of asuitable translucent, vertically disposed screen structure S, theprojecting light beam passingtherethrough in order to reach theaudience, and the projectors P2 and P3 being used alternately as wellunderstood. As illustrated, Veach projector comprises a lamp house 25, amechanism housing 26 and a film magazine 21. Each projector preferablycornprises a wide-angle lens combination such, for example, as describedand claimed in the copending Bowen applications Serial No. 316,403,filed November 1, 1928, and Serial No. 420,937, filed January l5, i930.With such wide-angle lens combinations, the distance between the screenand projectors is much less than is necessary with an ordinaryprojection lens and, ac-

cordingly, rear projection is rendered practical in the limited spaceusually existing on the stage of an ordinary theatre.

In Fig. 8, the line L2 is the center line of the screen structure S.This line is disposed at right angles with respect to the screenstructure and intersects the center thereof. The projectors P2 and P3are disposed, respectively, at opposite sides of said line L2, theoptical axis L3 of the respective projectors being obliquely related tothe screen structure S. The projectors P2 and P3 are shown,respectively, as having motion picture films A2 and A2 disposed thereinand each of these films, assuming horizontal disposition of the sheet onwhich the drawings are made, travels vertically with respect to itsprojection field or aperture and is disposed at right angles to theoptical axis of its projection lens.

Under such circumstances, the image on the screen structure S may not beproperly focused in one or both of the side areas thereof for the reasonthat the light paths from either projector to opposite sides of thescreen structure are dissimilar in length. However, in accordance withmy invention, the film trap assembly of each projector mechanism may beconstructed and arranged as herein described, or in an equivalentmanner, so that each section of the film A2, as it passes through itsprojection aperture, is obliquely related, as at a2, to its projectionaxis `and each section of the iilm A3, as it passes through itsprojection aperture, is obliquely related, as at a3, to its projectionaxis. When the aforesaid oblique relation of the films is properlyobtained, it results that there is obtained proper or satisfactory focusof the image throughout the area of the screen structure S.

In connection with Fig. 8, it is to be noted that the film trap assemblyarranged as heretofore described in Figs. 2--7 is adaptedlfor use withthe projector P2. This appears from a consideration of Fig. 6 whereinthe adjustment is such that the iilm F is obliquely related in vaclockwise sense to the optical axis of the associated projection lens.To adapt the film trap assembly of said Figs. 2-7 for use with theprojector P2 of Fig. 8, the adjust- ,ment should be such that the film Fis obliquely related in a counter-clockwise sense to the optical axis ofthe associated projection lens. Under the circumstances last recited,the respective positions of the wheels 5 and B should be the reverse ofthat shown in Fig. 6.

With the film trap assembly in normal position as shown in Figs. 3 and5, the passage-defining members H, i4 and l5 may be adjusted by propermanipulation of the screws i9 and I9a so as to move substantially abouta vertical axis as defined by the screws i8 and iBa al1 as hereinbeforedescribed. In this manner, the path for the film through the projectionaperture may be chosen as desired either clockwise or counterclockwise,Fig. 6, with respect to that path which is at right angles with respectto the line L3. As stated, the proper adjustment is thus eected when theprojector is to one side or the other of a line intersecting the screenat right angles to the center thereof.

In the event that the projector is positioned a. substantial distanceeither above or below the aforesaid center line of the screen, it may bedesirable to compensate for improper image focus on the screen structurebecause of this relation. This may be accomplished within limits withthe form of mechanism herein described. Thus, should the projector bepositioned well above said screen center line, the screw |80. may berevlso tracted and the screw I8 advancedwhereby the projection apertureis moved about a horizontal axis vwith resultant correction oftheimagefocus.

Further, it shall be understood that the adjustment may be universal inthe sense that the projection aperture may be adjusted about averticalaxis as dene'd by the screws I8 and I8a, and also about ahorizontal axis as just described.

With the form of my invention herein described, the passage-formingmember I5 may -readily be removed so that there maybe substitutedtherefor a similar member with an aperture'of diilerent area. As welland as stated, the. .passageform ing members I4 and I5 may be replacedby a single member which is adjusted as-hereinbefore described inconnection withv the member I4 or in an equivalent manner. This singlemember may be adapted to slidably or otherwise receive one `or moreplates with apertures of diiferent areas whereby the projector may beadapted for use with different types of nlm. Since the passage-formingmember I I is springseated and since the passage-forming member I4coacts therewith to maintain the springs for said member II under moreor less tension, it results that said passage-forming members Il and I8tend to'and do grip that lm section in alinement with the projectionaperture in a' yielding manner, whereby the film is held under tension.This is an advantageous feature vof my invention. This nlm tensioningphase of the invention, it shall be understood, is not to be limited tothose arrangements wherein the aforesaid oblique relation of the lmsection obtains since the nlm may be variably tensioned in a desiredmanner by an arrangement such as herein described, or the equivalentthereof, when that film section -in alinement with the projectionaperture is disposed, as in present commercial practice, at right angleswith respect to the axis of the projection lens. Y

It is well understood in the projection art that, in the absence ofcorrective measures,` a keystone eiect exists on the screen when theaxis of the projecting light beam is in non-coinciding relation withrespect to the screen center line, i. e. that line which intersects thecenter of the screen and is disposed at right angles with respectthereto. Thus, in Fig. '9, if the projection aperture of the projectorP3 is rectangular as indicated by the broken lines at 3B, the border ofthe image area on the screen structures denes a keystone, 'as indicatedby the broken lines at Sila, this result obtaining due to the provisionof the rectangular apertureand further due to the fact that the axis ofthe projecting light beam is obliquely related to said screen structureS as shown in Fig. 8. f

To vavoid this keystone effect of the border of Bthe image area, theprojection aperture of the projector P3 may itself dene a keystone asindicated bythe full lines at 3l, Fig. 9, the latter keystone beingoppositely related to the keystone 3Go as produced by a rectangularprojection aperture. Accordingly, with a keystone projection aperture asindicated at 3 I, Fig. 9, the periphery of the image area on the screenstructure S defines substantially a rectangle as shown at 3 Ia, Fig. 9.With the form of my Ainvention herein shown, the passage-forming memberi5 denes the projection aperture as stated above and, under suchcircumstances, this member I5 preferably has the keystone configurationshown at 3 I, Fig. 9. In connection with my invention, -it is to benoted that the keystone effect of the screen image area border 'may beovercome otherwise than as stated above. Thus, if thelmis caused to passthrough the projection eldin some 4position such as indicated at A2,Fig.- l, the keystone, eiect of the image area border maybe wholly orpartly overcome, thisposition lbeing obtained with the form of myinvention hereinshownby proper manipulation of. thefscrewsy I9, I9ar.Ordinarily, however, the keystoneieiect is not-eliminated as just statedbecauser with the arrangementshown, such a position. ofthe lm intheprojectionneld results in an undesired focus condition.. f

While the invention zhas been described 'with respect to a certainparticular preferred example which gives satisfactory. results, it Willibe understood by those skilled in the artjafter understanding theinvention, that various changes and modifications' may be made. withoutdeparting -from the spirit and 4scope oftheinvention and it is intendedthereforexin 'the appended .claims to cover all such .changes and-modi'cations.

.What is vclaimed-as new and desiredto bese-A cured by Letters'Patentis:v

l. In a device of the character described, the combination with anobjective lens,offpassage` forming mechanism for guidinga filmalong apath intersecting a light beam .traversing said objective lens, andmeanscarried by-fsaid mechanism forobliquelyrelating. said lm to the opticalaxis ot said objective lens, said means being movable with respect tosaid mechanism and coacting directly with said film..

2. In a device of the character described, the combination withan'objectivelens, of separable members for guiding a nlm valong a pathintersecting a lightbeam traversing said objective lens, and meanscarried by said members for obliquely relating said nlm to thevopticalaxis of said objective lens, said means being movable withrespect to said members and coacting directly with said lm. r l

3. In a device of the character described, the combination with anobjective lens, 'of separable members for guiding-a lm along a pathintersecting a light beam traversing said objective lens, and meanscarried by said members for obliqueiy relating said lm to the opticalaxis of said objective lens, said means-comprising a passage-formingmember defining the projection aperture of said device. y

4. In a projector, the combination with the lm trap assembly havingmembers movable with respect to each other, of passage-forming memberscarried by saidfirst named members respectively, said passage-formingmembers dening the path of movement of a motion picture lm through theprojection eld of said projector, and means for adjusting said.passage-forming mem# bersy with respect to said rst lnamed members.`

5. In a projector, -the combination with the film trap assembly havingmembers movable with respect to each other, of passage-forming memberscarried by said rlrst named members respectively, said passage-formingmembers defining the path of movement of a motion picture nlm throughthe projection eld of said projector, and means for adjusting said'passage-forming'fmembers with respect to said rst named members abouteither a substantially horizontal or a substantially'vertical'axis.

6. In a projectonthe combination with the lfilm trap assembly havingmembers movable with respect to each other, of passage-forming memberscarried by said rstnamed members respectively, saidpassage-forming-members dening the path of movement of a motion picturefilm through the projection iieid of said projector, means for adjustingone of said passage-forming members with respect to the axis of saidprojection field, and means for biasing another o! said passage-formingmembers toward said one passage-forming member.

7. In a projector, the combination with the nlm trap assembly havingmembers movable with respect to each other, of passage-forming memberscarried by said rst named members respectively, said passage-formingmembers dening the path of movement of a motion picture film through theprojection field of said projector, means for adjusting one of saidpassage-forming members about either a substantially vertical or asubstantially horizontal axis with respect to the axis of saidprojection iield, and means for biasing another of said passage-formingmembers toward said one passage-forming member.

8. In a projector, the combination with the iilm trap assembly havingmembers movable with re spect to each other, of passage-forming memberscarried by said rst named members respectively, said passage-formingmembers defining the path of movement of a motion picture nlm throughthe projection iield of said projector, means for adjusting one of saidpassage-forming members with respect to the axis oi said projectionneld, said means comprising a pair of screws threaded to one of saidfirst named members and another pair of screws extending loosely throughsaid one of said rst named members, and means for biasing another ofsaid passage-forming members toward said one passage-forming member.

JOSEPH D. BASSON.

